Internal combustion engine with fan system

ABSTRACT

In an internal combustion engine cooling system, wherein a fan with an adjustable cooling performance is provided with a fan wheel having a hub with radial fan blades pivotally supported on the hub, a control piston is disposed in the hub and connected to the blades for the pivot position adjustment thereof over a range from a suction position to a blowing position including a neutral position in which the blades are oriented in a plane including the axis of rotation of the fan wheel under the control of a control unit causing movement of the piston for pivoting the blades to a position for a cooling performance adjusted to the engine requirements. The system is simple, safe and efficient and permits counter flow operation of the fan for cleaning purposes.

BACKGROUND OF THE INVENTION

The invention relates to an internal combustion engine with a fan system including a fan wheel with adjustable fan performance.

Such adjustable fan systems are known in the art, particularly in a form wherein the fan wheel is operated in a temperature-dependent manner for example via a viscous clutch or another way in which the fan speed is adjustable relative to the speed of the internal combustion engine driving the fan. Also, solutions are known wherein a separate drive is provided for the fan wheel, for example an electric motor whose speed can be controlled independently of the speed of the internal combustion engine.

Other air moving systems, which include a fan wheel which is adjustable for controlling the fan performance and wherein for changing the performance not only the fan speed is adjustable but also fan blades are provided which are angularly adjustable in an active or passive manner. The adjustability of the fan blades with active admission of air to the fan blades is in connection with air movers, as they are known for example from EP 0 945 676 A2, not limited to a change of the blade angle while maintaining the moving direction of the air but also the direction of moving the air may be reversible. If, in the process the fan blades are turned beyond a direction transverse to the direction of rotation, a reverse flow can be generated with small changes of the annular positions of the fan blades about the pivot axis normal to the direction of rotation of the fan wheel.

It is desirable to control the fan wheels of this type in particular with regard to the setting of the blade angles depending on the desired cooling performance in such a way that an instantaneous adaptation of the blade angles to the desired cooling performance is achieved. On the other hand, the respective blade angle corresponding to the desired cooling performance should be obtained as accurately as possible and with little control requirements using, in particular, control data already available in the engine control system and also high operational safety should be maintained.

SUMMARY OF THE INVENTION

In an internal combustion engine cooling system, wherein a fan with an adjustable cooling performance is provided with a fan wheel having a hub with radial fan blades pivotally supported on the hub, a control piston is disposed in the hub and connected to the blades for the pivot position adjustment thereof over a range from a suction position to a blowing position under the control of a control unit causing movement of the piston for pivoting the blades to a position for a cooling performance adjusted to the engine requirements. The system is simple, safe and efficient and permits counter flow operation of the fan for cleaning purposes.

For an accurate adjustment of the pivot angle of the blades to obtain the desired cooling performance, the control movement of the control piston for adjusting the respective blade angles is needed. The actual determination of the axial position of the control piston in the hub in accordance with a momentary blade angle adjustment is determined in accordance with the invention via a measuring arrangement assigned to the fan wheel hub. As such a measuring arrangement a Hall sensor is particularly suitable, specifically a Hall sensor arrangement with a magnet arranged on the control piston and a sensor arranged preferably fixed outside the fan wheel hub. It is particularly advantageous and cost-effective if the sensor arrangement is provided on the non-rotating part of the supply structure for the fluid admitted to the control piston which extends into the fan wheel hub. In this way, for the magnet as well as the sensor mounting means are provided which are not critical as far as space considerations are concerned and which can be realized by simple means possibly even by cementing.

With the possibility to exactly determine the respective position of the control position, the blade angle position which corresponds directly to the position of the control piston and also the rotational speed of the fan wheel which is driven by the engine via the control unit of the internal combustion engine, the fan performance can be accurately tuned to the desired cooling performance. This can be achieved under the control of a performance graph or with some computer operation via a control unit in which the operational data of the internal combustion engine are available which are needed to determine the desired cooling performance. They are combined with the data defining a position value of the control piston corresponding to the respective momentary blade angle position. In this way from these values the position of the control piston and consequently the blade angle setting can be directly adapted to the desired cooling performance by a corresponding fluid admission to the control piston.

With respect to the transmission of the digital control data which are available to the engine control unit and the generally analog control of the control valves it has been found expedient if the data to be transmitted from the engine control unit to the fan control unit are transmitted in the form of a PWM (Pulse Width Modulated) signal which is representative of the desired cooling performance and which facilitates a direct assignment to the respective blade angle to be set in a simple manner via the value thereof. The assignment is expediently so selected that the minimum value of 0% corresponds to the maximum blade angle and the maximum value corresponds to the minimum blade angle. In accordance with the invention, the data are transmitted via a CAN bus system which is generally already present.

In connection with the present invention, of the whole adjustment range for the blade angle, that is, the adjustment range between its end position for suction and its end position for blowing, only a part range is utilized for the operation of the blades during adjustment to the desired cooling performance of the fan. This partial range extends for a fan wheel whose blades are adjusted between suction and blowing operation or vice versa across a transverse orientation relative to the direction of rotation of the fan wheel, only over a section which is disposed between an end position of the control piston and a position corresponding to the operating position in which the flow generated by the blades is reversed. In particular with blades which can be pivoted beyond a position of the blades transverse to the direction of rotation of the fan the overall adjustment range can be kept relatively small. The adjustment range used for the setting of the blade angle to achieve the desired cooling performance is about 40 to 50°. The blade angle is about 10 to 20° for minimum cooling requirements and 40-50° for maximum cooling requirements.

Consequently, only a part of the range over which the blade angle is adjustable in accordance with the control path length of the control position is used for a sufficiently accurate adjustment of the blade angle by means of a corresponding sufficiently accurate control of the control piston by means of the control valves. For the control valves the opening times and the closing times can be predetermined based on a respective control impulse, but the time periods may also be adjustable. This can be done in particular in connection with a throttling effect in order to achieve a uniform and smooth position adjustment with a view to minimizing wear and also avoiding the generation of vibrations.

With Hall sensors for determining the position of the control piston, also the speed of the fan wheel can be determined without incurring additional expenses. Although the speed of the fan wheel is determined via the engine control unit for providing a desired cooling performance and is taken into consideration in the information supplied to the control unit, the determination of the speed via the fan wheel by the Hall sensors with corresponding information supplied to the engine control unit has been found expedient since in this way it can be determined directly whether the fan wheel is in fact driven as expected and at a speed corresponding to the speed of the internal combustion engine.

The invention further resides in a cooling system for an internal combustion engine with a fan wheel whose speed is controlled depending on the level of the desired cooling performance as determined to be necessary for the internal combustion engine with regard to the engine speed and operating condition. This control is preferably dependent on a respective previous setting in a control circuit in which the respective momentary blade angle is adapted to the desired blade angle and deviations are corrected by controlling the control fluid inlet or outlet valves. An examination of the correction of the setting of the blade angle to the desired blade angle may also be used as a functional examination of the inlet and the outlet valve or at least the valve block comprising the inlet and outlet valve.

The control circuit operates with an actual position and desired position comparison for the blade angle. When the comparison shows a value which differs from the desired value for the vane angle another pass of the control circuit is initiated. For the duration of the control procedure a time limit is provided and a system error is determined if the time limit is exceeded.

The time limit is preferably in the range of about 10 to 30 sec, in particular at values where deviations from the desired cooling performance are not critical. Consideration is also given to the predetermined opening and closing times of the control valves which are a fraction of the time limit, that is about 15 milliseconds, if the time limit is for example 15 sec.

In connection with such tuned time periods, there are sufficient rest periods in which the system of pressure driven and/or spring-supported control piston and fan blades held at the respective blade angles are stabilized even with sudden jerk-like adjustment steps, so that a sufficiently accurate determination of the respective actual blade angle is possible. The determination of the blade angle in comparison with the desired blade angle may also be used for a determination of a proper functioning of the control valves.

The invention will become more readily apparent from the following description of a particular embodiment thereof with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partial representation of a fan wheel,

FIG. 2 shows an arrangement of a fan wheel in a position between a piston internal combustion engine used as a drive motor and a cooler wherein, by changing the blade angle of the fan wheel, the cooler performance is adjustable and the air flow direction of the fan is reversible for operation of the fan selectively in blower or suction direction,

FIGS. 3-5 show the fan wheel schematically with different blade angle settings,

FIG. 6 shows a characteristic performance graph for the relation of the blade angle with respect to a PWM signal corresponding to a desired cooling performance of the internal combustion engine, and

FIG. 7 shows schematically the fan wheel and the control arrangement provided for controlling the blade angle of the fan blades.

DESCRIPTION OF A PARTICULAR EMBODIMENT

FIG. 1 shows a part of a fan wheel 1 in a schematic sectional view. The axis of rotation of the fan wheel 1 is indicated by the reference numeral 10. Concentrically with the axis of rotation 10 the wheel 4 is arranged with its pot-shaped hub body 5, which has a bottom wall 6, a hub wall 7 and a cover 8 covering the inner space 9 of the hub. In the hub wall 7, the foot sections 3 of the fan blades 2 are supported so as to be rotatable about pivot axes 23 disposed in a plane extending normal to the axis of rotation 10 of the hub 4. In the inner space 9 of the hub body 5 which is closed by the cover 8 a control piston 11 is disposed so as to be axially movable in the direction of the axis of rotation 10. The piston 11 has a piston bottom 13 arranged opposite the cover and having a piston wall 12 extending parallel, and adjacent to, the hub wall 7. An annular gap between the piston wall 12 and the hub wall 7 is sealingly bridged so that an operating chamber 16 is formed between the piston bottom 13 and the cover 8. A supply line 14 extends to the operating chamber 16 via a rotational penetration 17 which is concentric with the pivot axis 10. Opposite the operating chamber 16, to which an operating fluid can be admitted, the operating piston 11 is elastically supported on the bottom wall 6 by means of compression springs 20, which, as shown in FIG. 1, are disposed in spring pockets 19 formed in the operating piston 11. Several such spring pockets 19 are provided over the circumference of the operating piston 11. The operating piston 11 however may be supported by other axial support elements which are spring-like.

The fan blades 2, which are pivotable about their respective axes of rotation 23, are rotatably supported by their respective foot sections 3 and bearings 21 mounted in the hub wall 7. Axial support is provided by means of a support plate 22 onto which the respective foot section 3 is mounted and which is provided, eccentrically with respect to the axis of rotation 23, with an actuating pin 24 projecting into a recess 25 in the wall 7 the control piston. The recess 25 may be in the form of a dead end bore or an annular groove.

With the eccentricity of the actuating pin 24 relative to the pivot axes 23 of the respective fan blades 2, an axial displacement of the control piston in the direction of the axis of rotation 10 of the fan wheel 1 results in a rotation of the fan blades 2 about their respective pivot axes 23.

The axial displacement of the piston is achieved by admitting an operating fluid under pressure, in particular pressurized air to the operating chamber 16. The pressurized air is supplied to, and/or released from, the operating chamber 16 via the rotational penetration 17 preferably through a supply line 14 including control valves 54, 55 or similar. FIG. 1 further indicates the presence of a measuring arrangement 26 for detecting the axial position of the control piston 11 and consequently, indirectly also of the pivot position of the fan blades 2 relative to the pivot axis 23. As a result, the angular position 33 of the blades can be detected. The control piston 11 is biased by the operating fluid in one direction against the force of a spring support, for example, coil springs 20 by which the piston 11 is movable in the opposite direction. FIG. 2 shows, in a highly schematic way, the arrangement of such a fan wheel between an internal combustion engine 18 and a cooler 27 disposed in front of the internal combustion engine 18. Depending on the pivot position of the fan blades 2 with respect to the pivot axis 23, the fan wheel 1 operates with a suction mode according to arrow 28 moving air toward the internal combustion engine 18 or in a blowing mode, that is, moving air in the direction of the arrow 29 toward the cooler 27 in order to blow deposits or debris or dust off the cooler 27. The direction of rotation of the fan wheel 1 is the same in both modes of operation that is during suction operation (arrow 28) and blowing operation (arrow 29) and is indicated by the arrow 30 so that in a radial view as, the fan wheel and the fan wheel blades move in a direction as indicated by the arrow 31 with the hub 4 appearing as shown in FIG. 2.

A fan blade position for suction operation (arrow 28) is shown in FIG. 2 for a fan blade 32 extending in the direction normal to the drawing plane. The respective blade angle is indicated by the numeral 33 and opens with respect to the shown angular position of the fan blade 2 opposite to the direction of rotation 31. The fan performance is determined by the size of the blade angle 33 based on the speed of the fan wheel 1. The performance during suction operation (arrow 28) increases with increasing fan blade angle 33. The switchover of the fan blade from suction operation to blowing operation occurs in accordance with the arrow 34 via a trans-verse orientation with respect to the direction of rotation 31 and occurs suddenly once the transverse position has been reached.

This is shown also in FIGS. 3-5, wherein essentially the same reference numerals are used. The FIGS. 3 and 4 concern the blade angle-controlled suction operation with regard to the cooling performance demand of the internal combustion engine wherein the respective blade angle is adjusted by the control piston 11 in accordance with the desired cooling performance. Herein the fan performance is tuned to the cooling performance so that a cooling operation with optimal efficiency is achieved, that is with minimal power requirements of the internal combustion engine for the cooling.

FIG. 5 shows the blade position during blowing operation. This position is reached when the fan blade 32 in accordance with FIG. 2 is pivoted beyond the transverse position with respect to the circumferential direction in accordance with the arrow 34. In this range, the blade angle is also dependent on the respective position of the control piston 11 but the position of the control piston 11 is not controlled by applying pressure fluid to the piston operating chamber 16 depending on the desired cooling performance. Rather the control piston 11 is moved to an end position that is the end pivot position of the fan blades for blow-cleaning the radiator.

The data needed for the setting of the fan performance corresponding to the cooling performance required by the internal combustion engine 18 are generally present in the engine control unit 50. FIG. 6 shows for a fan wheel operating at a speed corresponding to that of the internal combustion engine 18 a control for the setting of the fan blade angle 33 for the fan blades 2, 32 corresponding to the engine requirements.

At times the control data corresponding to the cooling performance demand are already processed in such a way that they are available as signal of a signal strength corresponding to the desired cooling performance. This applies in particular to solutions where a fan wheel is controlled by a viscous clutch by which the speed of the fan wheel is controlled depending on strength of the control signal. In this solution for example a PWM signal of a signal strength corresponding to the desired cooling performance is supplied to the control unit 51, by which the pressure application to the control piston 11 for the setting of the fan blade angle position for obtaining the desired cooling performance is controlled taking into consideration that the speed of the fan wheel 1 is at a certain predetermined, in particular fixed, ratio to the speed of the internal combustion engine.

In such an arrangement, the speed of the fan wheel 1 may for example be the same as the speed of the internal combustion engine with a corresponding drive connection to the crankshaft of the internal combustion engine. If a particular transmission is interposed, for example, a belt drive, another but still fixed, speed ratio may be provided.

Of the fan blade angle range 53 basically usable for the setting of the cooling performance—as shown in FIG. 3—that is, in the range from a blade position transverse to the axis of rotation 10 of the fan wheel 1 in which the blades 2, 32 are oriented in the direction of rotation 31 of the fan wheel to a direction of a plane which includes axis of rotation 10, only a part range of the adjustability of the blades is used for controlling the fan to generate the cooling performance required by the internal combustion engine. This part range which is apparent from the schematic representation of FIGS. 3 and 4 extends in the exemplary representations of FIGS. 3 and 4 between a blade angle of 13° and a blade angle of 45° wherein the cooling performance increases with increasing blade angle. Herein the larger blade angle which corresponds to the larger fan performance represents the maximum needed cooling performance and, vice-versa, the smaller blade angle corresponds to the lowest needed cooling performance.

In accordance with this relationship, the PWM (Pulse Width Modulated) signal 52 is supplied to control unit 51 and, as shown for example in the performance graph of FIG. 6, depending on the strength of the PMW signal 52, a particular blade angle (FW) is predetermined. In FIG. 6, the blade angle is provided in relation to the PWM signal strength on a % basis. 100% corresponds to the smallest blade angle of the used blade angle range and consequently the smallest cooling performance according to a minimum cooling performance required by the internal combustion engine 18. Vice versa, a signal strength of 0% corresponds to the maximum blade angle of the blade angle range used and consequently, the maximum fan performance in accordance with a maximum cooling performance needed by the internal combustion engine.

Herein the control unit 51 controls the control valves 54, 55 by which fluid, in particular air, is admitted to the control piston 11 in accordance with the opening and closing times of the control valves. Here, the control valve 54 is the inlet valve and the control valve 55 is the outlet valve. The control lines assigned to the control valves are designated by the reference numerals 56 and 57. Starting with the control valves, fluid is supplied to the operating chamber 16 via the rotational penetration 17, see FIG. 1, where, as part of the measuring arrangement 26, the sensor 35 of a Hall sensor arrangement 36 is arranged. The sensor arrangement includes a magnet 37 which is disposed on the bottom wall 13 of the control piston 11 or is integrated into piston 11, for example disposed in a pocket thereof.

FIG. 7 shows further that the measuring arrangement 26 in particular in the form of a Hall sensor arrangement 36 detects the position of the control piston 11 and consequently the angular pivot position of the fan blades and provides a corresponding confirmation signal 58 to the control unit 51 which then supplies a confirmation signal back to the engine control unit.

FIG. 7 also shows that the measuring arrangement 26 particularly in the form of a Hall sensor arrangement 36 also detects the rotational speed of the fan wheel 1 which information may also be supplied to the control unit 51 as indicated by the line 60. By comparison of the speed of the fan wheel 1 determined in this way with the fan speed as determined by the engine control unit 50 on the basis of the engine speed, it can be examined whether the parameters processed by the engine control unit 50 and used for the PWM signal supplied to the control unit 51 concerning the blade angle have resulted in a corresponding result. Discrepancies between the speed of the fan wheel 1 as determined by the engine control unit 50 and the speed signal supplied via the line 60 as confirmation signal permit an examination of the signal chain including the control valves 54, 55 disposed in the signal chain. As a result, the measuring arrangement 26, particularly in its form as a Hall sensing arrangement 36, makes a functional examination with regard to a consistency of the desired cooling performance on one hand and the corresponding fan performance on the other hand possible without any additional expenditure.

Based on such an arrangement of an internal combustion engine 18 with a fan system which includes a fan wheel 1 with adjustable blades 2 and a cooling system for an internal combustion engine with a fan wheel assigned to the fan system of the internal combustion engine, a control arrangement would be expedient based on the value of the PWM signal supplied by the engine control unit 50 to the control unit 51 which signal corresponds to the desired cooling performance and the corresponding fan performance. If this condition and, consequently, a sufficiently accurate determination of the blade angle are fulfilled, a total time available for passing a control circuit path is provided. If this is not acknowledged by an actualized return signal received by the engine control unit, a new control pass with determination of the PWM signal value is initiated. The time generally available for passing the control circuit begins, after the conversion of the PWM signal to the respective blade angle, with a comparison of the blade angle as desired blade angle with the actual blade angle. If deviations are found, depending on the determination whether the actual blade angle is too large or too small, the release valve or the supply valve is energized for adjusting the control piston 11.

Preferably, fixed opening and closing times are provided for the respective control valves. It may however also be expedient to operate with opening and closing times which depend in each case on the size of the desired adjustment of the blade angle. This is true particularly for the control of the control valves for operating ranges which are outside the range in which the fan performance is controlled dependent on the desired cooling performance, which is also determined by the desired cooling performance, by changing the blade angle position.

The blade angle set during a control procedure by operation of the control valves 54, 55 is used in the control unit as an actualized return signal for an actualized PWM signal. Preferably, the blade angle is again detected following a pause. This forms the basis for a further actual position-desired position comparison of the blade angle based on which, in the case of differences, a new pass through the control circuit is initiated.

Changes in the blade angle with respect to the setting thereof before the initiation of a possibly necessary correction by a control of the control valves in comparison with the setting after the correction by the control of the valves are used in the control circuit as signals for an examination whether the control valves combined in a valve block have worked in accordance with the provided values or whether errors have occurred in the operation of the control valves and/or in the control valves themselves wherein the predetermined waiting time facilitates also a determination of possible leakages by improperly closing valves.

The invention is, in particular in connection with such a control, of particularly simple design which satisfies also high safety requirements. Engine damages as a result of failure of the cooling system or malfunctioning of the cooling system can be avoided. The system operates with high efficiency and offers the possibility to be used in a suction mode as well as in a blowing mode for the removal of deposits or dust from the radiator. 

1. An internal combustion engine with a fan system including a fan wheel (1) having an adjustable cooling performance and an engine control unit (50) providing control data for the cooling performance of the fan needed for cooling the internal combustion engine (18) or a cooling circuit comprising the internal combustion engine (18), said fan wheel (1) including a fan wheel hub (4) with radial fan blades (2) pivotally supported on the hub (4) and including a control piston (11) axially movably disposed in the hub (4) and connected to the fan blades (2) for pivoting the fan blades (2), the fan blades (2) being pivotable over a range including a switch-over neutral position in which the blades (2) are oriented in a plane including the axis of rotation of the fan wheel (1), so that the fan wheel (1) is adjustable to blow in either axial direction depending on the pivot position of the blades at one or the other side of the switchover neutral position, a measuring arrangement (26) for determining the position of the control piston (11) in the hub (4) and, as a result, the pivot positions of the blades (2), a fan control unit (51) in communication with the measuring arrangement for recording the actual pivot position of the fan blades (2) and comparing it with a desired blade position which is determined based on engine operating conditions for providing a desired cooling performance with a certain blade angle position, the fan control unit (51) providing, upon detecting a deviation between the actual and the desired pivot position of the fan blades (2), an input signal for adjusting the fan blade pivot position.
 2. The internal combustion engine according to claim 1, wherein control valves (54, 55) are provided for controlling the admission of fluid to the piston (11) in the hub (4) and for the release of the fluid for adjusting the pivot position of the fan blades (2), the control signal for adjusting the blade pivot position being supplied to the respective control valve (54, 55).
 3. The internal combustion engine according to claim 1, wherein the measuring arrangement includes a Hall sensor arrangement (36) with a magnet (37) disposed on the control piston (11) so as to be movable with said control piston (11) and said fan wheel hub (4) and a position sensor (35) stationarily supported adjacent the fan wheel hub (4) for sensing the speed of the fan wheel (1) and the position of the piston (11).
 4. The internal combustion engine according to claim 1, wherein the desired cooling performance of the fan wheel (1) is determined based on the engine speed and various engine operating conditions.
 5. The internal combustion engine according to claim 2, wherein the desired cooling performance is provided as an input signal with a signal strength weighted over the performance spectrum and established in relation to the blade pivot position in one of a computerized, graphic and performance graph-based manner such that a minimum signal strength of the input signal corresponds to a maximum blade angle position for maximum cooling performance whereby, upon signal failure, the fan blades are in a maximum cooling performance position.
 6. The internal combustion engine according to claim 1, wherein the input signal is a PWM (Pulse Width Modulated) signal which is in a relationship with the blade angle position in such a way that a low PWM value of 0% corresponds to one blade pivot angle end position and a high value of 100% of the PWM signal corresponds to the opposite blade pivot angle end position, the blades (2), upon pivoting from one to the other end position, and vice versa, moving through their neutral position.
 7. The internal combustion engine according to claim 6, wherein the one or the other blade pivot angle end position corresponds to the end position of the control piston (11) which it assumes when no pressurized fluid is applied thereto while the respective other or one blade pivot angle end position corresponds to the end position of the control piston (11) when subjected to full pressure.
 8. The internal combustion engine according to claim 1, wherein the respective blade angle is formed by the angle of the blade (2) established between a plane normal to the axis of rotation of the fan wheel (1) and the angle of the blades (2) relative thereto.
 9. The internal combustion engine according to claim 3, wherein the Hall sensor arrangement is provided so as to sense the position of the control piston (11) and the speed of the fan wheel (1).
 10. The internal combustion engine according to claim 2, wherein the control valves (54, 55) are 3/2-way inlet and outlet valves.
 11. The internal combustion engine according to claim 9, wherein the Hall sensor arrangement (36) includes a speed transmitter for the fan wheel (1).
 12. The internal combustion engine according to claim 11, wherein the speed of the fan wheel (1) assigned to the respective desired cooling performance is monitored via the Hall sensor arrangement (36) acting as speed signal transmitter.
 13. A cooling system for an internal combustion engine with a fan system including a fan wheel (1) having an adjustable cooling performance and an engine control unit (50) providing control data for the cooling performance of the fan needed for cooling the internal combustion engine (18) or a cooling circuit comprising the internal combustion engine (18), said fan wheel (1) including a fan wheel hub (4) with radial fan blades (2) pivotally supported on the hub (4) and including a control piston (11) axially movably disposed in the hub (4) and connected to the fan blades (2) for pivoting the fan blades (2), the fan blades (2) being pivotable between opposite end positions over a range including a neutral switch-over position in which the blades (2) are oriented in a plane including the axis of rotation of the fan wheel (1) so that the fan wheel (1) is adjustable to blow in either axial direction depending on the pivot position of the blades (2) at one or the other side of the neutral switch-over position, a measuring arrangement (26) for determining the position of the control piston (11) in the hub (4) and, as a result, the pivot positions of the blades (2), a fan control unit (51) in communication with the measuring arrangement for recording the actual pivot position of the fan blades (2) and comparing it with a desired blade position which is determined based on engine operating conditions for providing a desired cooling performance with a certain blade angle position, the fan control unit (51) providing, upon detecting a deviation between the actual and the desired pivot position of the fan blades (2), an input signal for adjusting the fan blade pivot position said fan wheel (1) having a cooling performance which is variable and adjustable dependent on the respective speed and the operating conditions of the internal combustion engine under the control of a control signal determined on the basis of the desired cooling performance.
 14. The cooling system according to claim 13, wherein the adjustment of the fan wheel (1) to the desired cooling performance occurs based on a previous setting in a control circuit in which the respective blade angle is compared to the desired blade angle and deviations are corrected by controlling the inlet and outlet valves (54, 55) wherein an examination of the correction of the setting of the blade angle to the desired blade angle is used as a functional examination of the inlet and outlet valves (54, 55).
 15. The cooling system according to claim 14, wherein the control circuit ends in an actual position—desired position comparison for the blade angle wherein, with values deviating from the desired blade angle, a new pass through the control circuit is initiated and wherein for the comparison an overall time limit is predetermined, which, when exceeded, results in a system error indication.
 16. The cooling system according to claim 15, wherein, in accordance with the predetermined overall time for the passage of the control circuit and the—within the given overall time—relatively small displacement travel of the control piston (11), a fixed response time is provided for the inlet and outlet valves (54, 55) which is a fraction of the overall time.
 17. The cooling system according to claim 13, wherein the control circuit (51) is part of a control arrangement (50) for which, at an input, a signal value for the desired cooling performance or, respectively, the desired blade position, in particular a PWM signal value, is determined and a transition to the control circuit within a given overall time occurs only if the signal exceeds a predetermined minimum value. 